1. Field of the Invention
The present invention relates to a method and an apparatus for making monolayers of particles or molecules and, more particularly, to such methods and apparatuses suited for large scale production industries.
2. Description of the Prior Art
In today's high technology industry, the miniaturization of electronic circuitry, high-density storage of information, screen display and other devices are reaching sub micrometer level. Decades ago, several methods were invented to achieve small devices and proved to be performing in the sub-millimeter level like smearing, spreading, shearing, microtomization, extrusion or passing between rollers to thin down. While these methods are approaching the micrometer scale, defects are likely to occur like holes, bumps, disorientation, cracks, etc. The production of layers by sublimation of material under vacuum is interesting for inorganic material, and nanometer thick layers were made. Unfortunately, this obliges the use of elevated temperature for metals that destroy fragile material like proteins or magnetic clusters that could be involved in the process. Moreover, the orientation or more generally the organization of matter in such approaches is not possible, atoms or molecules being piled up at random one above the other.
Therefore, it has been proposed to drive particles onto flat planes and packing them side-by-side to construct layers. The organization of matter in such thin layers yields interesting properties in optics, electronics, bio detection, filtration, magnetic storage devices, etc. Indeed, the size of the objects to be manipulated can be anywhere between 1 millimeter and one tenth of a nanometer. Therefore, through the decades, several 2D assembly methods were invented in order to achieve such organization, but most of them proved to be unsuitable for large scale production industries.
The first 2D assembly method was invented at the beginning of the XXth century. It simply consisted in depositing particles onto a flat gas-liquid interface and bringing them together with mobile barriers to form a monolayer. Initially thought as being uniform and defect free, the monolayers being made of particles approached from every direction led to holes and local collapses in the monolayer.
Canadian Patent Application No. 2,291,825 published on Dec. 3, 1998, discloses a method and an apparatus for preparing monolayers of particles. More particularly, this document discloses a Dynamic Thin Laminar Flow (DTLF) method wherein a liquid film, containing a suspension of particles, is injected onto a rotary cylinder. The rotation of the cylinder pushes the particles one against the other to form a continuous monolayer on the rotary cylinder. The rotary cylinder is advanced longitudinally with respect to a substrate on which the monolayer is deposited. According to this method, mechanical devices are necessary to produce the driving force required to bring the particles one against the other. Moreover, the dimensions of the rotary cylinder limit the size of the monolayer that can be produced with this method. The rotary cylinder also contributes to limit the monitoring zone required to control the production of the monolayers.
Although the method described in the above-mentioned patent application is efficient, it has been found that there is a need for a new method and apparatus, which offers flexibility in production while allowing for easier monitoring and control thereof.